1. Field of the Invention
The present invention relates to an air conditioning system, and more particularly to an air conditioning system for variably controlling the operating capacity of a plurality of compressors in accordance with a cooling or heating load in a room, and a method for controlling the air conditioning system.
2. Description of the Related Art
Generally, an air conditioning system is an appliance for cooling or heating a room using a refrigerating cycle of a refrigerant compressed by compressors.
The compressor includes a compression unit provided with a compression chamber for compressing the refrigerant, and a motor unit for variably changing the capacity of the compression chamber. In order to meet a trend towards large scale and multi-function applications, the air conditioning system has been developed to comprise two compressors or an inverter-type compressor so that the total capacity of the compressors can be variably changed in accordance with a cooling or heating load in a room, thereby reducing a power consumption rate required to operate the compressors.
FIG. 1 is a schematic view of a conventional air conditioning system in a cooling mode. FIG. 2 is a schematic view of the conventional air conditioning system in a heating mode.
As shown in FIGS. 1 and 2, the conventional air conditioning system comprises first and second indoor heat exchangers 2 and 12 for heat-exchanging a refrigerant with air in a room, thereby cooling or heating the room, first and second outdoor heat exchangers 4 and 14 serving as condensers for condensing the refrigerant in case that the first and second indoor heat exchangers 2 and 12 function as coolers, while serving as evaporators for evaporating the refrigerant in case that the first and second indoor heat exchangers 2 and 12 function as heaters, first and second compressors 6 and 16 for compressing the refrigerant from a low-temperature and low-pressure gaseous state into a high-temperature and high-pressure gaseous state in order to supply the high-temperature and high-pressure gaseous refrigerant to the first and second indoor heat exchangers 2 and 12 or the first and second outdoor heat exchangers 4 and 14, a first expansion device 8 arranged between the first indoor heat exchanger 2 and the first outdoor heat exchanger 4 to expand the refrigerant into a low-temperature and low-pressure state, a second expansion device 18 arranged between the second indoor heat exchanger 12 and the second outdoor heat exchanger 14 to expand the refrigerant into a low-temperature and low-pressure state, and a control unit (not shown) for controlling operation of the first and second compressors 6 and 16. The first indoor heat exchanger 2, the first compressor 6, the first outdoor heat exchanger 4 and the first expansion device 8 are connected by a first refrigerant pipe 9, and the second indoor heat exchanger 12, the second compressor 16, the second outdoor heat exchanger 14 and the second expansion device 18 are connected by a second refrigerant pipe 19.
The reference numerals 7 and 17 respectively denote direction change valves adapted to change the flow direction of the refrigerant so that the air conditioning system can be operated in a cooling or heating mode. The direction change valves 7 and 17 are respectively connected to suction lines 6a and 16a and discharge lines 6b and 16b of the first and second compressors 6 and 16, and controlled by the control unit so that the cooling and heating modes of the air conditioning system are selectively established via a single refrigerating cycle of the refrigerant.
That is, the direction change valves 7 and 17 are required to allow the air conditioning system to have both cooling and heating functions. Thus, an air conditioning system having only a cooling function does not require the direction change valves 7 and 17.
Now, the operation of the above-described conventional air conditioning system will be described in detail.
In case that the air conditioning system is operated in a cooling mode and a cooling load in a room to be eliminated is large, as shown in FIG. 1, the control unit operates both of the first and second compressors 6 and 16, and a high-temperature and high-pressure refrigerant discharged from the first and second compressors 6 and 16 is transferred to the first and second outdoor heat exchangers 4 and 14. When the refrigerant passes through the first and second outdoor heat exchangers 4 and 14, the refrigerant is heat-exchanged with the peripheral air, thereby being condensed from a high-temperature and high-pressure gaseous state into a high-temperature and high-pressure liquid state. Then, the condensed refrigerant in the high-temperature and high-pressure liquid state is transferred to the first and second expansion devices 8 and 18. When the condensed refrigerant passes through the first and second expansion devices 8 and 18, the refrigerant is expanded into a low-temperature and low-pressure state and then introduced into the first and second indoor heat exchangers 2 and 12. When the expanded refrigerant passes through the first and second indoor heat exchangers 2 and 12, the refrigerant is heat-exchanged with indoor air, thereby absorbing heat and then being evaporated into a gaseous state. Here, the first and second indoor heat exchangers 2 and 12 function as coolers.
In case that the air conditioning system is operated in the cooling mode and a cooling load in the room to be eliminated is small, the control unit operates only the first compressor 6. A refrigerant discharged from the first compressor 6 circulates along the first outdoor heat exchanger 4, the first expansion device 8, the first indoor heat exchanger 2 and the first compressor 6. Here, the first indoor heat exchanger 2 functions as a cooler.
On the other hand, in case that the air conditioning system is operated in a heating mode and a heating load in a room to be eliminated is large, as shown in FIG. 2, the control unit operates both of the first and second compressors 6 and 16, and a high-temperature and high-pressure refrigerant discharged from the first and second compressors 6 and 16 circulates in the opposite direction of the circulation of the refrigerant in case that that the air conditioning system is operated in the cooling mode and the cooling load to be eliminated is large. Here, the first and second indoor heat exchangers 2 and 12 function as heaters.
In case that the air conditioning system is operated in the heating mode and a heating load in the room to be eliminated is small, the control unit operates only the first compressor 6. A refrigerant discharged from the first compressor 6 circulates along the first indoor heat exchanger 2, the first expansion device 8, the first outdoor heat exchanger 4 and the first compressor 6. Here, the first indoor heat exchanger 2 functions as a heater.
The conventional air conditioning system comprising the first and second compressors 6 and 16 copes with only the current amount of the cooling or heating load in the room. Accordingly, since it is difficult for the conventional air conditioning system to rapidly cope with the variation of the cooling or heating load, the conventional air conditioning system has a limit in improving comfortableness in a room. Further, the conventional air conditioning system comprises two cycles, thus having low cooling and heating efficiency.
In order to rapidly cope with the variation of the cooling or heating load, there has been proposed another conventional air conditioning system comprising a single large-capacity inverter-type compressor (not shown) instead of the first and second compressors 6 and 16. Such a conventional air conditioning system employs the expensive inverter-type compressor and an inverter circuit, thus increasing the production cost.